On June 24, 1999, about 1220 Alaska daylight time, a wheel equipped Maule M-4-220C airplane, N40677, sustained substantial damage during a forced landing about 7 miles northeast of McGrath, Alaska. The airplane was being operated as a visual flight rules (VFR) personal flight when the accident occurred. The solo airline transport pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was the continuation of a cross-country flight that originated at the Willow Airport, Willow, Alaska, about 0930. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on June 24, the pilot reported that his planned destination was Nikolai, Alaska, with a brief stop in Takotna, Alaska. He said that the flight between Willow and Takotna was uneventful. The pilot reported that after takeoff from the Takotna Airport, he climbed the airplane to about 1,500 feet msl. He said that about 15 minutes after departure, the engine began to run rough, and lose power. The pilot said that while performing the engine emergency procedures, he smelled smoke in the cabin, and selected a forced landing area on a river bank bordered by trees. During the landing roll, the airplane's left wing collided with a stand of trees, the airplane pivoted 180 degrees to the left, and the left main landing gear collapsed. The airplane sustained substantial damage to the wings, fuselage, and empennage. The airplane owner recovered and transported the airplane wreckage to the Anchorage International Airport. A Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office, examined the airplane wreckage on July 13th. The inspector reported that the top portion of the number four engine cylinder was separated between the cylinder barrel and the cylinder head, and added that the piston connecting rod was fractured.